1. Field of the Invention
The present invention relates to a disk drive, a disk drive controlling method and a disk drive controlling program, and, in particular, to a disk drive having a capability of properly handling a gravity center deviated disk, a disk drive controlling method for properly handling a gravity center deviated disk, and a disk drive controlling program for executing the method.
2. Description of the Related Art
A disk recording medium such as a CD has an information recording track (hereinafter, simply referred to as a ‘track’) or tracks on which data is recorded via a read/write head (optical pickup in a case of CD), as well known. Such a track is formed spirally in general, and, in many case, this spiral is not an exact concentric one by reason concerning, for example, an accuracy of the center hole of the disk, a circularity of the disk, or so. Therefore, during rotation of the disk in a disk drive for reading/reproducing data recorded thereon, a misalignment may occur between an optical pickup (in the case of CD) of the dirk drive and the relevant track of the disk. A tracking error signal, simply abbreviated as a TE signal hereinafter, as well known, indicates such a misalignment, and has a magnitude in proportion to the amount of the detected misalignment.
Either a gravity center deviated disk or an eccentric disk may cause such a misalignment phenomenon. The eccentric disk is a disk in which the track on the disk has shifted with respect to the proper spiral one, and, even in such a case, by a tracking servo control, a proper information reading/writing operation may be achieved on the disk as long as the amount of the eccentricity exceeds a predetermined threshold. However, in a case of the above-mentioned gravity center deviated disk, in which the gravity center of the disk is shifted from the exact rotation center thereof, an abnormal vibration may occur thereon which may obstruct proper information reading/writing operation on the disk with the optical pickup. In order to avoid such a situation, it is necessary to lower the disk rotation speed in case the disk currently loaded is the exocentric gravity center disk.
However, it is difficult in general to determine whether such a misalignment occurring between the optical pickup and the track on the disk is caused by the reason that the disk is a gravity center deviated disk or an eccentric disk.